Ground detector



1 1,490,371 P" 15 1924' A. c. FINNEY GROUND DETECTOR Filed April 20. 1921 frm/entor Alfred C. Finn y His' Attorney- Patented AR. 15, 1924.

PATENT OFFICE.

ALFRED C. IEINNEY, OF SCHENECTADY, NEW YORK, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

GROUND DETECTOR.

Application filed April 20, 1921.

To all whom it may concern:

Be it known that I, ALFRED C. FINNEY,

a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Ground Detectors, of which the following is a specification.

My invention relates to ground detectors and has for its object to provide means operative continuously for detecting and indicating the location and character of grounds on an electric system without interfering with the otherwise normal operation of the system.

In the operation of rolling mills in steel plants, considerable water is usually present as leakage from hydraulic control apparatus and also as waste from the water used to cool the rolls. Conditions are, therefore, very favorable for grounds and with the great amount of metal, that is to say good conducting material, present, it becomes highly desirable at all time to know instantly without interrupting the rolling operation whether a ground is present and, if so, its location and character, otherwise operation may be continued under conditions dangerous not only to the apparatus but also to the operators. Other dangerous conditions, especially in shape mills, arise when a piece of steel in the rolls gets temporarily out of control as in the case of cobbles. Before the mill can be stopped, the piece forming the cobble is apt to twist and squirm in all directions with the possibility of striking live conductors or other electrical apparatus used in driving the mill and thereby causing grounds. My invention is particularly applicable for the detection of grounds on electrically driven rolling mill systems. although its application is not limited, to this relation of utility.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Fig. 1 illustrates diagrammatically an embodiment of my invention; Fig. 2 illus- Serial No. 462,819.

trates diagrammatically a modification of my invention; and Fig. 3 illustrates diagrammatically another modification of my invention.

In Fig. 1, there is shown a fly-wheel m0- tor-generator set arranged to supply the motors of a rolling mill or other load apparatus. The arrangement shown comprises an alternating current circuit 1 supplying a motor 2 which is preferably directconnected to a plurality of direct current generators 3 by a shaft 1 on which is mount ed a fly-wheel 5. The generators 3 are shown arranged alternately in a seriescircuit with a plurality of motors 6 which drive a rolling mill or other machinery 7.

In order to have a continuous indication asto the presence of grounds, the location and character thereof if any occur on this system, I provide in a circuit 8 across one of the dynamo-electric machines, for instance in the form of my invention shown in Fig. 1, one of the motors 6, a control means or electro-responsive device 9. The form of control means I prefer to use is of a type known in the art as a differential relay and in the example shown comprises two windings 10 and 11 arranged in series with the circuit 8 to control the movement of contact controlling members 12 and 13. The circuit 8 is grounded at a point 14 inter mediate the windings 10 and 11. The windings 10 and 11 operate with a differential action to move the contact controlling members 12 and 13 by armatures 15 and 16 pivotally related to a lever 17 which is fulcrumed at a point 18 and carries the contact controlling members 12 and '13. The contact controlling members 12 and 13 are arranged to bridge contacts 19 and 20 respectively and thereby to control circuits including signaling means 21 and 22 respectively. The signaling means 21 and 22 may be such as to give either audible or visible signals or both, such as, for instance, whistles, bells or lamps or a combination thereof, but for the purposes of my invention, I shall hereinafter refer to signaling means 21 and 22 as white and blue lamps respectively. Since the signaling means '21 and 22 are controlled by the differential each of the motors 6 is 900 volts.

action of the windings 10 and 11, either one or the other of the signaling means 21 and 22 will be operated on the occurrence of a ground on the system in accordance with the voltages on the windings '10 and; 11 coincident with such ground.

For showing the voltage on one of the windings and thus indicating the location and character of grounds on the system, there is in shunt with the circuit 8 across the winding 11 an indicating means or voltmeter V. In order to facilitate the location of grounds, the voltmeter V may have, in addition to the usual graduations, markings such asA, B, C, D, E, etc., corresponding to various points at which grounds might occur.

For the purpose of illustration, the operation of my ground detector, as shown in Fig, 1,will be described on the basis of a practical example in which the direct electrometive force of each of the generators 3 is 600 Volts and the counter electromotive force of Grounds will be assumed at different points A, B, C, D, and Eon the system, the voltage drops across windings 10 and 11 and the operation of the signaling means 21 and 22 pointed out. The voltage drop across winding 11 is at all times indicated by the voltmeter V.

N 0 ground on the system.

Assuming first normal conditions, that is no ground on the system, the voltage across each of the windings 10 and 11 of control means 9 is the same and the voltmeter V will indicate 450 volts. The windings 10 and 11 will, therefore, be equally energized, holding the lever 17 in a balanced position and neither of the circuit controlling members 12 and 13 will be moved to circuit closing position. Consequently, neither of the lamps 21, 22 will be lighted.

Ground at A.

lighted.

Ground at B.

l/Vith a good ground on the system, as at B, the voltage across winding 10 will be 900 volts and across winding 11 indicated by the voltmeter V, zero. Consequently, winding 10 will be energized .andcircuit controlling member 13 moved to bridge contacts 19, thereby completing the circuit of signaling means or white lamp 21 and causing the same to be lighted.

G'rotmd at 0.

With a good ground on the system, at C, the voltage across winding 11, indicated by the voltmeter V will be 900 volts and across winding 10, zero. Consequently winding 11 will be energized and circuit controlling member '13 moved to bridge contacts 20, thereby completing the circuit of signaling means or blue lamp 22 and causing the same to be lighted.

Ground at D.

Ground at E.

Vi ith a good "round on the system at E, the voltage across winding 11, indicated by the voltmeter V, will. be 1200 volts and across winding 10, 300 volts. Therefore, winding 11 will be more strongly energized than winding 10 and consequently will overcome the effect of winding 10 and move circuit controlling member 13 to bridge contacts 20,

thereby completing the circuit of signaling means or blue lamp 22 causing the same to be lighted.

Therefore, if there is a good ground on the system, it will be definitely indicated as at one of the three points A, C or E by the lighting of the blue lamp 22 or at one of the two points B or D by the lighting of the white lamp 21 and for the particular one of the points A, B, C, D or E by the voltmeter reading corresponding to a good ground at that point.

For grounds in general, the following table shows the readings of the voltmeter V or voltages across winding 11, voltages across winding 10 and the indications of the signaling means 21 and 22 for a range from a ground of no resistance, that is a good ground, up to a gnmnd of infinite resistance, that is no ground. This table or one of similar form may be furnished with equipn'ients embodying my invention and the voltmeter V may be marked A, it, C, D, E, etc., at the voltages corresponding to good grounds at positive and in the opposite direction as negative.

Voltages across s fi fg fi Winding 10. Location of Lamp ground. lighted.

With ground resistance.

Zero Infinite. Zero. Infinite.

........ 450 --450 None. 600 450 -300 450 Blue;

0 450 9(]0 450 White 900 450 0 450 Blue. 300 450 600 450 White 1, 200 450 300 -450 Blue.

It is obvious that the better the ground, that is the lower the resistance of the ground, the more dangerous it will be to continue operation and therefore the more desirable it is to have a definite indication of the location and character of such a ground. As heretofore pointed out my invention gives a definite indication on the occurrence of a good ground on the system.

It will also be evident from the preceding table that with the blue lamp lighted and the voltmeter reading substantially 900 volts, there may be a ground of appreciable resistance at E or a good ground at C.-

Likewise with the blue lamp lighted and the voltmeter reading substantially 600 volts, there may be a ground of appreciable resistance at either C or E or a good ground at A. Similarly with the white lamp lighted and the voltmeter reading substantially 300 volts, there may be a ground of appreciable resistance at'B or a good ground at D. With the white lamp lighted and the voltmeter readingsubstantially zero, there is a good ground at B and with the blue lamp lighted and the voltmeter reading substantially 1200 volts, there is a good ground at E. If the voltmeter reads substantially 300, 600 or 900 volts, the operator is warned to look for a good ground at one of the points D, A or C, respectively, and although in the event of the vol"- meter reading 300, 600 or 900 volts, there may be a ground of appreciable resistance at the points B, C, or E, the operator knows nevertheless when and where to look for a good ground. It is also clear that the nearer the voltmeter reads to 450 volts, the greatervide in series with a circuit 8 across one of the dynamo electric machines, for example, one of the motors 6, two preferably equal resistances 10 and 11". The circuit 8 is provided with a ground connection it intermediate the resistanceslO and 11 and in shunt with the circuit 8 across one of the resistances, for example, resistance 11, there is a voltmeter V for indicating the location and character of grounds on the system. The voltmeter V may have, in addition to the usual graduations, markings such as A, B, C, D, E, etc. to facilitate the location of grounds.

0n the basis'that the motors 6 and generators 3 rate the same eleetromotive forces assumed in connection with the description of the operation of the form of my invention shown in Fig. 1, it is obvious that the voltmeter V will indicate the same voltages as before for similar conditions and the voltages across resistances 10 and 11" will be the same as tabulated for windings l0 and 11 respectively of Fig. 1. Therefore, if voltmeter V indicates substantially 0, 800, 600, 900, or 1200 volts, the operator is warned tolook for a good ground at one of the points B, D, A, C, or E respectively, although as heretofore explained, if the voltmeter reads substantially 300, 600 or 900 volts, there is not necessarily a good ground at D, A, or C respectively. Also, as heretofore pointed out,if the voltmeter reading differs from 450 volts by a small amount, a ground of high resistance character is indicated at some one of the points A, B, C, D, or E.

In Fig. 3, I have shown a modification of my invention with the shunt circuit 8 connected across one of the motors 6 of a system comprising a plurality of motors and generators alternately connected in series as shown in Figs. 1 and 2. Electro-respon sive means or relays 23 and 24 have their windings 10 and 11 connected in series with the shunt circuit 8 which is provided with a ground connection 14; intermediate the windings 10 and 11. I may also includein series with the shunt circuit 8 and windings 10 and 11, if the latter are of relatively low resistance, resistances 25 and 26 which, if desired, may be made adjustable for varying the pick-up points of relays 23 and 24!:- If desired, however, the relays 23 and 2% may be provided with relatively high resistance windin s and the resistances 25 and 26 omitted. lielay 23 operates to control the circuit of signaling means 21' by contact controlling member 12 which is arranged to bridge contacts 19 and relay 24 operates to control the circuit of signaling means22 by contact controlling member 13 which is arranged tobridge contacts 20. In shunt with the circuit 8 across the windings of one of the relays, for example winding 11 of relay 24 and its correspond- EEO &

ing resistance 26,-there is a voltmeter V for indicating the location and character of grounds. The voltmeter V may have, in addition to the usual graduations, markings A, B, C, D, E, etc. to facilitate the location of grounds.

In the modification of my invention shown in Fig. 3, and 011 the basis that the motors and generators ofthe system rate the electrom otive forces heretofore assumed, the relays 23 and 24 are set to respond to a predetermined voltage between 450 and 600 volts. for windings 10 and 11 of Fig. 1, it will be clear that under like conditions the same voltages will occur across winding 10' and resistance 25 and across winding 11 and resistance 26 respectively and therefore the voltmeter will indicate as heretofore explained.

It will be noted from the tabulated voltages that the pick-up points for relays 23 and 24 come within a voltage range, that is 450 to 600 volts, such that upon the occurrence of a ground on the system only one of the relays can respond at a time. Thus for a ground at A, C or E, relay 24 will operate to control the circuit or signalling means or blue lamp 22 and for a ground at B or D, relay 23 will operate to control the circuit of signaling means or white lamp 21. It is'also obvious from the tabulated voltages that, if the relays 23 and 24 are set to respond to voltages somewhat greater than 450 volts, signaling means 22 will be operated by relay 24 upon the occurrence of either a low or high resistance ground at A, C or E andsignaling means 21 will be operated by relay 23 upon the occurrence of either a low or high resistance ground at B or D, whereas if the relays 23 and 24 are set to respond to voltages somewhat less than 600 volts, signaling means 22 will be operated by relay 23 upon the occurrence of a good ground at A, C, or E or a ground of appreciable resistance at C or E and signaling means 21 will be operated by relay 24; uponthe occurrence of a good ground at B or D or a ground of appreciable resistance at B. In any event, the operator is warned to look for a good ground at A, C,-or E by the lighting of the blue lamp 22 or at B or D by the lighting of the white lamp 21 and the reading of the voltmeter V will indicate at which one of the points A. B, (l, D, or E a good ground may be. 7

Although I- have shown and described my invention in considerable detail, I do not wish to be limited to the specific details thereof, as shown and described, but may use such modifications, substitutions, or equivalents thereof, as are embraced within the scope of my invention.

What I claim as new and desire to se-:

Referring to the voltages tabulated cure by Letters Patent of the United States, is 1 1. 4L ground detecting s stem comprising the combination with a plurality of sources of direct and counter elcctromotive forces alternately connected in a series circuit of a shunt circuit across one of said sources, ieaus adapted to produce a voltage drop proportional to the current therethrough connected in series with said shunt circuit, a ground connection for said shunt circuit at an intermediate point in said voltage drop producing means, and means connected. in circuit to measure the voltage drop between said iutermdiate point and one terminal of said shunt circuit.

2-. A. ground detecting system comprising the combination with an odd number of dynamo-electric machines consisting of motors and generators alternately arranged in a series circuit, of a shunt circuit across one of whichever of said machines occurs in an even number, signaling means, differential eiectro-responsivc means in series with said shunt circuit connected to be controlled in response to the differences in potential between a ground on the system and the terminals of the machine across which said shunt circuit is connected to operate said signaling means, and means connected in circuit with said electro-responsive means for measuring one of said differences in potential.

3. A ground detector for an electric system wherein an odd number of sources of direct and counter electromotive forces are connected in a series circuit and wherein each of said direct electromotive forces has the same value and each of said counter electromotive forces has the same value, comprising a shunt circuit across one of whichever of said sources occurs in an even number, signaling means, a ground connection for said shunt circuit, means comprising two windings connected in series with said shunt circuit for controlling said signaling means in response to grounds on said system, and means for measuring the drop in voltage across one of said windings for grounds at different points of the system.

4. A ground detecting system comprising the combination with a plurality of dynamoelectric machines consisting of motors and generators alternately connected in a series circuit, said motors rating equal counter electromotive forces and said generators rating equal direct electromotive forces, of a shunt circuit across one of said dynamoelectric machines, electro-responsive means in series with said shunt circuit, a ground connection at an intermediate point in said electro-responsive means, signaling means adapted to be controlled by said electro-responsive means and means for measuring the difference in potential between said intermediate point and one terminal of said shunt circuit.

A ground detector comprising the combination with a plurality of sources of direct and counter electromotive torces'connected alternately in a series circuit, of a circuit connected in shunt across the terminals or" one of said sources and provided with a ground connection, signaling means, electro-responsive means provided with two windings connected in series with said shunt circuit on opposite sides of said ground connection operative in response to the difierence between the differences in potential between said ground connection and said terminals to control said signaling means, and means connected in shunt with one of said windings for indicating the voltage thereon.

6. A ground detector comprising the combination with two motors and three generators alternately connected in a series circuit, each of said motors rating the same counter electromotive force and each of said generators rating the same direct electromotive force, of a circuit connected in shunt with one of said motors, two' windings connected in series in said shunt circuit, a ground connection for said shunt circuit intermediate said windings, signaling means, and means acted upon by said windings operative in response to a difierence in forces exerted by said windings to control said signaling means.

7. A ground detector comprising the combination with two motors and three generators alternately connected in a series circuit, each of said motors rating the same counter electromotive force and each of said generators rating the same direct electromotive force, of a circuit connected in shunt with one of said motors, two windings connected in series in said shunt circuit, a

ground connection for said shunt circuit intermediate said windings, signaling means, and means acted upon by said windings operative in response to a difference in forces exerted by said windings to con trol said signaling means, and means connected in circuit to measure the voltage drop across one of said windings.

8. In a system of the class described wherein two motors each rating the same counter electromotive force are connected alternately in series with three generators each rating the same direct electromotive force, a ground detector comprising a shunt circuit across one of said motors, a difierential relay having two windings connected in series in said shunt circuit, a ground connection for said shunt circuit intermediate the windings of said relay, signaling means controlled by said relay, and a voltmeter connected in shunt with one of the windings of said relay.

9. In combination with an electric system wherein two motors each rating the same counter electromotive force are connected alternately in series with three generators each rating the same direct electro motive force, a ground detector comprising a shunt circuit across one of said motors, signaling means, electro-responsive means comprising two windings connected in series in said shunt circuitoperative in response to predetermined voltage conditions to control said signaling means, a ground connection for said shunt circuit intermediate said windings, and means for indicating the difference in potential between said ground connection and one of the terminals of said shunt circuit.

In witness whereof, I have hereunto set my hand this 19th day of April, 1921.

ALFRED C. FINNEY. 

